Refi my primary home to payoff rental?

[Emily Snow]

I own one rental property. It is in my name, not an LLC. Rent is not my sole source in income. Both loans have about 20 years remaining.

Primary residence: $940

Rental payment:  $740

Total payments (primary+rental) per month: $1680

Rent due: $1340

In an effort to increase monthly cash flow, I'm looking into refinancing one or both loans.  $ wise, it will be the least expensive (interest rate) to refinance my primary home to a 30 year mortgage, with enough cash out to payoff the rental property.

That would change my total combined payment (including taxes and insurance for both properties) to $1300ish, giving me $380 more per month.

Dollarwise that makes sense in an instant.  But here are my concerns/questions:

-Is it dangerous to put all the debt burden on my primary residence?  If so, how dangerous? 

-Are there tax advantages to having a mortgage on my rental property?  Will I lose or gain an advantage by having all the interest paid be on my primary home? (I am able to itemize every other year by shifting charitable donations from Dec 31 to Jan 1)

-Would it be better to refinance my primary home to a 20 year loan (I only have 20 years left anyway) and the rental back to a 30 year loan...and keep them separate?  The current refi rate on the rental would be .75% lower and the primary home would be about .875% lower than it currently is.

My eventual plan, 2-4 years, is to refinance to purchase another rental.